An Experimental Analysis of the Basic Phenomena Involved in Modern Diffraction Theories

摘要

This study utilizes direct experimental techniques to analyze the basic scattering mechanisms that are important to modern diffraction theories. The efforts are intended to supplement and guide the development of theoretical models by exploring parameter ranges and configurations that are intuitive extensions of the cases handled by current prediction techniques. A broad program of experimental investigation of rigid three-dimensional scatterers is presented. The thin prolate spheroids is used as a basic model for scattering from smoothly curved bodies. Baffles, cylinders, cones, and cone variants serve for an examination of edges and tips of various orders. In addition to standard pulse measurements with gated receivers, some data are obtained by a holographic imaging technique. The results show that the backscattered pressure from smoothly curved bodies is determined almost exclusively by specular effects, even at wavelengths that are relatively large compared to the appropriate dimensions of the scatterers. Small changes in or additions to the smooth surface, however, modify both the amplitude and directivity of the scattering. The Freedman theory of echo formation is carefully derived, and its predictions are compared with applicable experimental results.